1. Field of the Invention
The present invention relates to a light emitting diode (LED) package. More specifically, the present disclosure relates to an LED package having an increased brightness and a liquid crystal display (LCD) device including the LED package.
2. Discussion of the Related Art
Liquid crystal display (LCD) devices, which are advantageous in displaying moving images and widely used for the displays of portable devices, computers and televisions due to their high contrast ratio, display images based on optical anisotropy and polarization of liquid crystal molecules.
An LCD device has a liquid crystal (LC) panel that may include two substrates having two electrodes thereon and a liquid crystal layer between the two substrates. The arrangement direction of the liquid crystal molecules in the liquid crystal layer may be adjusted by changing the electric field generated between the two electrodes, and the transmittance of the liquid crystal layer is thus changed to display various images.
However, since the LCD device does not include an emissive element, an additional light source is required to display an image. Thus, a backlight unit including a light source is typically disposed on a rear surface of the LC panel.
Although a fluorescent lamp such as a cold cathode fluorescent lamp (CCFL) or an external electrode fluorescent lamp (EEFL) has been used as a light source of the backlight unit, the fluorescent lamp has been replaced with a light emitting diode (LED) that has advantages in power consumption, weight and brightness in accordance with the need for LCD devices of thin profile and lightweight.
The backlight unit may be classified into a direct type and an edge type according to a position of the light source. In the direct type backlight unit, since the light source is disposed under the LC panel, the light emitted from the light source is directly supplied to the LC panel. In the edge type backlight unit, since a light guide plate is disposed under the LC panel and the light source is disposed on at least one side surface of the light guide plate, the light emitted from the light source is indirectly supplied to the LC panel using refraction and reflection in the light guide plate. The direct type backlight unit has advantages in image quality and clarity as compared with the edge type backlight unit.
Since the light emitted from the LED has a relatively narrow emission region of high intensity, a large number of LEDs are disposed in the direct type backlight unit for supplying a uniform surface light to a display region of the LC panel. However, such an increase of the number of LEDs entails an increase of the fabrication cost of the LCD devices.
To reduce the fabrication cost, a lens for widening an emission region of the light from the LED has been developed and applied to the LED so that the light from the LED can be diffused to a wider region. Specifically, as the LCD device is applied for a desktop monitor and a wall-mountable television as well as a portable computer, the LCD device with low price, high quality, thin profile and wide display area, is preferred. As a result, the LCD device for which the fabrication cost is reduced with thin profile and high quality by reducing the number of LEDs has been researched.
FIGS. 1A and 1B are cross-sectional views showing a light emitting diode package according to the related art.
In FIG. 1A, a first LED package includes an LED 29a and a first LED lens 10. The first LED lens 10 includes a first curved surface 11 having a first curvature, a second curved surface 12 having a second curvature and a plane surface 13 connecting the first and second curved surfaces 11 and 12. A first light a1 emitted from the LED 29a enters the first curved surface 11 and is refracted at the first curved surface 11 to be a second light a2. In addition, the second light a2 is refracted again at the second curved surface 12 to be emitted as a third light a3.
The first LED lens 10 is a refractive type where the light of the LED 29a is emitted from the first LED package through refraction at the first and second curved surfaces 11 and 12. Since an irradiation angle of the first LED package is determined by a refractive index of the material used for the first LED lens 10, it is hard to obtain an irradiation angle over about 155 degrees when a typical material such as polymethylmethacrylate (PMMA) or polycarbonate (PC) is used for the first LED lens 10.
In FIG. 1B, a second LED package includes an LED 29a and a second LED lens 20. The second LED lens 20 includes a plane surface 21, a slanting surface 22, and a side surface 23 connecting the plane surface 21 and the slanting surface 22. In addition, the second LED lens 20 is a reflective type and has a symmetrical shape with respective to a central axis CA. A first central light b1 emitted from the LED 29a enters the plane surface 21 and is refracted at the plane surface 21 to become a second central light b2. In addition, the second central light b2 is totally reflected on the slanting surface 22 to be emitted through the side surface 23 as a third central light b3.
Since the second LED lens 20 has the plane surface 21 as an incident surface, an incident angle of the first central light b1 is relatively small as compared with a light entering a curved surface and it is hard to adjust a refracting angle of the second central light b2. As a result, the second LED lens 20 is formed to have a wide radius w so that the second central light b2 through the plane surface 21 can be wholly reflected on the slanting surface 22.
For example, when the second LED lens 20 has the radius w, a first stray light c1 which is emitted toward a portion relatively far from a center of the LED 29a may enter the plane surface 21 and may be refracted at the plane surface 21 to be a second stray light c2. In addition, the second stray light c2 may be totally reflected on the side surface 23 to be emitted through the slanting surface 22 as a third stray light c3. As a result, the light of the LED 29a may not be uniformly diffused and concentrated on a central portion.
To obtain a uniform diffusion, the radius w of the second LED lens 20 is required to be enlarged to a first radius w1 such that the second stray light c2 is totally reflected on the slanting surface 22 and is emitted through the side surface 23 to be a fourth stray light c4.
In addition, when the light from the LED 29a is widely diffused by expanding a width or an emission angle of the LED 29a, the radius of the second LED lens 20 is required to be enlarged. As a result, the parts cost and fabrication cost of the second LED lens 20 increase and the fabrication cost of the LCD device also increases.
Further, since a separation distance between adjacent LEDs 29a is fixed, there is limit in enlargement of the radius of the second LED lens 20. As a result, the LED package including the first and second LED lenses 10 and 20 has limit in increasing the irradiation angle.